This research proposes to study the effects of methylmercury on the growth and development of fetal brain. A genetically defined inbred strain of mouse, and organo-typic and dissociated cultures of mouse fetal brain and human fetal brain (obtained from hysterotomies) will be used. Pregnant animals will be given predetermined doses of methylmercury at specific stages of pregnancy. Offspring sacrificed at specified times will be studied with various morphologic technics including electronmicroscopy, immunocytochemistry, Golgi technics, radioautography and classical light microscopic stains. Both primary and secondary cultures of human and mouse fetal cerebrum and cerebellum will be exposed to various concentrations of methylmercury and the short and long term effects on sequential development of brain in vitro will be analyzed. The overall objectives of this proposal are to assess in detail the changes in development of fetal brain brought about by maternal intoxication of methylmercury, particularly the changes in the pattern of cell proliferation, neuronal migration, cortical differentiation and organization of cerebrum and cerebellum; to ascertain as fully as possible the mechanisms whereby these changes are brought about; and to correlate the findings with alterations observed in some of the developmental disorders of the nervous system encountered in man.